Solid propellant and gas generator charges or grains are currently used in many applications ranging from propulsion devices, such as rocket motors, to gas generators for inflation of gas bags or expulsion of rocket motors from launch tubes or for the generation of a fuel rich gas stream to be burned by a ducted rocket motor, for example. As used herein the term, "gas generator grain," will apply to any solid composition that is capable of self-sustained combustion to produce a gas stream regardless of whether that gas stream is subsequently used for propulsion, expulsion, or gas generating purposes.
Gas generating grains generally are classified as either end burning or internal burning. An end burning grain is one which is mounted within a combustion chamber provided with a suitable exhaust, ignited at one end; the burning surface then progressing to the other end at which point the entire grain is consumed. An internal burning grain is one which is provided with one or more ports along the length of the grain which, when ignited, burns either solely at these internal surfaces or, in some cases, a combination of the end surface and the internal surface. Internal burning grains have a greater degree of design flexibility since the rate at which the combustion gases are generated can be predictably determined by the design of the number and configuration of the ports. End burning grains, however, do not have such design flexibility, although they have the advantage of maximizing the amount of propellant that can be contained in any particular volume since there are no empty spaces for the ports.
A typical end burning gas generator grain exhibits what is known as a progressive pressure trace. This occurs because the gas evolution rate increases with burn time causing the pressure generated within the combustion chamber to increase with time. This characteristic is undesirable for many gas generator applications in which it is desired to have a relatively constant gas generation rate throughout a substantial portion of the burn time of the propellant grain.
According to this invention, I can control the gas generation rate of an end burning gas generator grain to produce a substantially constant gas generation rate. By applying a similar technique, I am also capable of selectively varying the gas generation rate through the burn time of the end burning gas generator grain. In addition, the technique by which the gas generation rate may be adjusted also permits the attainment of an improved bond between the gas generator and the liner or insulation which is interposed between the grain and the combustion chamber case.
It is accordingly an object of this invention to provide a method for controlling the rate of evolution of the gases produced by an end burning gas generator grain.
It is another object of this invention to provide an end burning gas generator having a substantially constant gas generation rate over a substantial portion of its burn time.
It is another object of this invention to provide a gas generator grain in which the rate of gas evolution is selectively varied during its burn time.
It is another object of this invention to provide a gas generator grain having improved bonding between the gas generator grain and the liner of the combustion chamber.
It is another object of this invention to provide a method for fabricating an end burning gas generator assembly.